1. Field of the Invention
The present invention relates to a motor driver that drives an electric motor of a valve timing adjusting apparatus of an internal combustion engine to adjust valve timing of at least one of an intake air valve and an exhaust valve of the engine.
2. Description of Related Art
It is often difficult to have a sufficient installation space for installing a valve timing adjusting apparatus at an internal combustion engine. In order to address the above difficulty, it has been proposed to divide and install electrical circuit elements (components) of a motor driver of the valve timing adjusting apparatus to multiple circuit boards, which are then stacked one after another. In this way, an available installation area for installing the electrical circuit elements is increased, and installability of the motor driver is improved. Japanese Unexamined Patent Publication No. 2006-37837 discloses one such technique, in which the electrical circuit elements of the motor driver are divided between a first circuit board and a second circuit board, which are then stacked one after another. Here, terminals of the first circuit board are welded to terminals of the second circuit board at opposed ends of the circuit boards to electrically connect the electrical circuit elements of the first circuit board to the electrical circuit elements of the second circuit board and also to achieve a sufficient fixing strength of each circuit board.
However, in the above technique disclosed in Japanese Unexamined Patent Publication No. 2006-37837, a positional relationship of each terminal at a first end side of the first circuit board with respect to the corresponding terminal at a first end side of the second circuit board differs from a positional relationship of each terminal at a second end side of the second circuit board with respect to the corresponding terminal at a second end side of the second circuit board. More specifically, each terminal at the first end side of the first circuit board and the corresponding terminal at the first end side of the second circuit board are arranged in this order in a predetermined direction, which is generally parallel to a plane of each circuit board, and each terminal at the second end side of the second circuit board and the corresponding terminal at the second end side of first circuit board are arranged in this order in the predetermined direction. Therefore, when each terminal at the first end side of the first circuit board is moved toward and is welded to the corresponding terminal at the first end side of the second circuit board, each terminal at the second end side of the first circuit board may possibly be spaced from the corresponding terminal at the second end side of the second circuit board to leave a substantial gap therebetween due to, for example, a manufacturing tolerance. In such a case, in order to weld each corresponding terminal at the second end side of the first circuit board to the corresponding terminal at the second end side of the second circuit board, at least one of these terminals needs to be deformed by applying a load thereto. This will possibly result in initial deformation of the terminal(s), which will then possibly result in ripping-off of the welded joint between the terminals after long term use.